Polymer Supported Nitrogen-Bridged Symmetrical Binuclear Dioxidomolybdenum(VI) Complexes and Their Homogeneous Analogues as Potential Catalysts for Efficient Synthesis of 2-Amino-3-Cyano-4H-Chromenes/Pyrans.

Reaction of 2-chloromethyl-1H-benzimidazole with known intermediates (i-iii), prepared from diaminoguanidine hydrochloride with salicylaldehyde, 5-bromosalicylaldehyde or 3,5-di-tert-butylsalicylaldehyde, in the presence of triethylamine (NEt3) led to the formation of benzimidazole appended new ligands, H4L1-H4L3 (I-III). The homogeneous nitrogen-bridged symmetrical binuclear complexes, [(MoVIO2)2(L1)(H2O)2] (1), [(MoVIO2)2(L2)(H2O)2] (2) and [(MoVIO2)2(L3)(MeOH)2] (3) have been isolated by reacting these ligands with [MoVIO2(acac)2] in a 1 : 2 molar ratio in refluxing methanol. Using 1 : 1 (ligand to Mo precursor) molar ratio under above reaction conditions resulted in the corresponding mononuclear complexes, [MoVIO2(H2L1)(MeOH)] (4), [MoVIO2(H2L2)(H2O)] (5) and [MoVIO2(H2L3)(MeOH)] (6). The binuclear heterogeneous compounds [(MoVIO2)2(L1)(DMF)2]@PS (PS-1), [(MoVIO2)2(L2)(DMF)2]@PS (PS-2) and [(MoVIO2)2(L3)(DMF)2]@PS (PS-3) have been obtained by immobilization of 1-3 onto chloromethylated polystyrene (PS) beads. All synthesized ligands, homogeneous as well as supported compounds have been characterized by elemental analyses and various spectroscopic methods. Single crystal X-ray diffraction study of complexes 1 and 3 confirms their nitrogen-bridged symmetrical binuclear structures while 4 is mononuclear. Heterogeneous compounds (PS-1-PS-3) have further been studied by microwave plasma atomic emission spectroscopy, X-ray photoelectron spectroscopy, and field emission scanning electron microscopy along with energy dispersive spectroscopy. These compounds (homogeneous and heterogeneous) were explored for catalytic applications to one-pot multicomponent reactions (MCRs) for efficient synthesis of biologically active 2-amino-3-cyano-4H-chromenes/pyrans (21 examples). Optimising various reaction parameters helped in achieving as high as 97 % yields of products. Though, only half equivalent of the binuclear complexes (1-3) was required compared to mononuclear analogues (4-6) to achieve comparable yields, heterogeneous catalysts have an added advantage due to their stability and recyclability. Suitable reaction mechanism has also been proposed based on isolated intermediates.

Controlled Modification of Triaminoguanidine-Based µ3 Ligands in Multinuclear [VIVO]/[VVO2] Complexes and Their Catalytic Potential in the Synthesis of 2-Amino-3-cyano-4H-pyrans/4H-chromenes.

Reaction of tris(2-hydroxybenzylidene)-triaminoguanidinium chloride (I·HCl) and tris(5-bromo-2-hydroxybenzylidene)-triaminoguanidinium chloride (II·HCl) with [VIVO(acac)2] (1:1 molar ratio) in refluxing methanol resulted in mononuclear [VIVO] complexes, [VIVO(H2L1')(MeOH)] (1) and [VIVO(H2L2')(MeOH)] (2), respectively, where I and II undergo intramolecular triazole ring formation. Aerial oxidation of 1 and 2 in MeOH in the presence of Cs2CO3 gave corresponding cis-[VVO2] complexes Cs[(VO2)(H2L1')] (3) and Cs[(VO2)(H2L2')] (4). However, reaction of an aerially oxidized methanolic solution of [VIVO(acac)2] with I·HCl and II·HCl in the presence of Cs2CO3 (in 1:1:1 molar ratio) gave mononuclear complexes Cs[(VO2)(H3L1)] (5) and Cs[(VO2)(H3L2)] (6) without intramolecular triazole ring formation. Similar anionic trinuclear complexes Cs2[(VO2)3(L1)] (7) and Cs2[(VO2)3(L2)] (8) were isolable upon increasing the amounts of the vanadium precursor and Cs2CO3 to 3 equiv to the reaction applied for 5 and 6. Keeping the reaction mixture of 1 in MeOH under air gave [VVO(H2L1')(OMe)] (9). Structures of 3, 7, 8, and 9 were confirmed by X-ray crystal structure study. A permanent porosity in the crystalline metal-organic framework of 7 confirmed by single-crystal X-ray investigation was further verified by the BET study. Along with a suitable reaction mechanism, these synthesized compounds were explored as effective catalysts for the synthesis of biomolecules 4H-pyran/4H-chromenes.

Catalytic, Antifungal, and Antiproliferative Activity Studies of a New Family of Mononuclear [VIVO]/[VVO2] Complexes.

Ligands derived from 2-(1-phenylhydrazinyl)pyridine and salicylaldehyde (HL1), 3-methoxysalicylaldehyde (HL2), 5-bromosalicylaldehyde (HL3), and 3,5-di-tert-butylsalicylaldehyde (HL4) react with [VIVO(acac)2] in MeOH followed by aerial oxidation to give [VVO2(L1)] (1), [VVO2(L2)] (2), [VVO2(L3)] (3), and [VVO2(L4)] (4). Complex [VIVO(acac)(L1)] (5) is also isolable from [VIVO(acac)2] and HL1 in dry MeOH. Structures of all complexes were confirmed by single-crystal X-ray and spectroscopic studies. They efficiently catalyze benzyl alcohol and its derivatives' oxidation in the presence of H2O2 to their corresponding aldehydes. Under optimized reaction conditions using 1 as a catalyst precursor, conversion of benzyl alcohol follows the order: 4 (93%) > 2 (90%) > 1 (86%) > 3 (84%) ≈ 5 (84%). These complexes were also evaluated for antifungal and antiproliferative activities. Complex 3 with MIC50 = 16 µg/mL, 4 with MIC50 = 12 µg/mL, and 5 with MIC50 = 16 µg/mL are efficient toward planktonic cells of Candida albicans and Candida tropicalis. On Michigan cancer foundation-7 (MCF-7) cells, they show comparable cytotoxic effects and exhibit IC50 in the 27.3-33.5 µg/mL range, and among these, 4 exhibits the highest cytotoxicity. A similar study on human embryonic kidney cells (HEK293) confirms their less toxicity at lower concentrations (4 to 16 µg/mL) compared to MCF-7.

Oxido-Molybdenum(V) Corroles as Robust Catalysts for Oxidative Bromination and Selective Epoxidation Reactions in Aqueous Media under Mild Conditions.

Two new meso-substituted oxido-molybdenum corroles were synthesized and characterized by various spectroscopic techniques. In the thermogram, MoO[TTC] (1) exhibited excellent thermal stability up to 491 °C while MoO[TNPC] (2) exhibited good stability up to 318 °C. The oxidation states of the molybdenum(V) were verified by electron paramagnetic resonance (EPR) spectroscopy and exhibited an axial compression with dxy1 configuration. Oxido-molybdenum(V) complexes were utilized for the selective epoxidation of various olefins with high TOF values (2066-3287 h-1) in good yields in a CH3CN/H2O (3:2, v/v) mixture in the presence of hydrogen peroxide as a green oxidant and NaHCO3 as a promoter. The oxidative bromination catalytic activity of oxido-molybdenum(V) complexes in an aqueous medium has been reported for the first time. Surprisingly, MoO[TNPC] (2) biomimics of the vanadium bromoperoxidase (VBPO) enzyme activity exhibited remarkably high TOF values (36 988-61 646 h-1) for the selective oxidative bromination of p-cresol and other phenol derivatives. Catalyst MoO[TNPC] (2) exhibited higher TOF values and better catalytic activity than catalyst MoO[TTC] (1) due to the presence of electron-withdrawing nitro groups evident from cyclic voltammetric studies.

Facile Synthesis of ß-Tetracyano Vanadyl Porphyrin from Its Tetrabromo Analogue and Its Excellent Catalytic Activity for Bromination and Epoxidation Reactions.

Complex 2,3,12,13-tetracyano-5,10,15,20-tetraphenylporphyrinatooxidovanadium(IV) {[VIVOTPP(CN)4], 2} has been prepared by nucleophilic substitution of ß-bromo groups of the corresponding 2,3,12,13-tetrabromo-5,10,15,20-tetraphenylporphyrinatooxidovanadium(IV) {[VIVOTPP(Br)4], 1} using CuCN in quinoline. Both complexes show biomimetic catalytic activity similar to enzyme haloperoxidases and efficiently brominate various phenol derivatives in the presence of KBr, H2O2, and HClO4 in the aqueous medium. Between these two complexes, 2 exhibits excellent catalytic activity with high turnover frequency (35.5-43.3 s-1) due to the strong electron-withdrawing nature of the cyano groups attached at ß-positions and its moderate nonplanar structure as compared to 1 (TOF = 22.1-27.4 s-1). Notably, this is the highest turnover frequency value observed for any porphyrin system. The selective epoxidation of various terminal alkenes using complex 2 has also been carried out, and the results are good, specifying the importance of electron-withdrawing cyano groups. Catalysts 1 and 2 are recyclable, and the catalytic activity proceeds through the corresponding [VVO(OH)TPP(Br)4] and [VVO(OH)TPP(CN)4] intermediates, respectively.

Mononuclear/Binuclear [VIVO]/[VVO2] Complexes Derived from 1,3-Diaminoguanidine and Their Catalytic Application for the Oxidation of Benzoin via Oxygen Atom Transfer.

Ligands H4sal-dag (I) and H4Brsal-dag (II) derived from 1,3-diaminoguanidine and salicylaldehyde or 5-bromosalicylaldehyde react with one or 2 mol equivalent of vanadium precursor to give two different series of vanadium complexes. Thus, complexes [VIVO(H2sal-dag) (H2O)] (1) and [VIVO(H2Brsal-dag) (H2O)] (2) were isolated by the reaction of an equimolar ratio of these ligands with [VIVO(acac)2] in MeOH. In the presence of K+/Cs+ ion and using aerially oxidized [VIVO(acac)2], the above reaction gave complexes [K(H2O){VVO2(H2sal-dag)}]2 (3), [Cs(H2O){VVO2(H2sal-dag)}]2 (4), [K(H2O){VO2(H2Brsal-dag)}]2 (5), and [Cs(H2O){VVO2(H2Brsal-dag)}]2 (6), which could also be isolated by direct aerial oxidation of complexes 1 and 2 in MeOH in the presence of K+/Cs+ ion. Complexes [(H2O)VIVO(Hsal-dag)VVO2] (7) and [(H2O)VIVO(HBrsal-dag)VVO2] (8) were isolated upon increasing the ligand-to-vanadium precursor molar ratio to 1:2 under an air atmosphere. When I and II were reacted with aerially oxidized [VIVO(acac)2] in a 1:2 molar ratio in MeOH in the presence of K+/Cs+ ion, they formed [K(H2O)5{(VVO2)2(Hsal-dag)}]2 (9), [Cs(H2O)2{(VVO2)2(Hsal-dag)}]2 (10), [K2(H2O)4{(VVO2)2(Brsal-dag)}]2 (11), and [Cs2(H2O)4{(VVO2)2(Brsal-dag)}]2 (12). The structures of complexes 3, 4, 5, and 9 determined by single-crystal X-ray diffraction study confirm the mono-, bi-, tri-, and tetra-anionic behaviors of the ligands. All complexes were found to be an effective catalyst for the oxidation of benzoin to benzil via oxygen atom transfer (OAT) between DMSO and benzoin. Under aerobic condition, this oxidation also proceeds effectively in the absence of DMSO. Electron paramagnetic resonance and 51V NMR studies demonstrated the active role of a stable V(IV) intermediate during OAT between DMSO and benzoin.

Trinuclear vanadium(iv) and vanadium(v) complexes derived from 2,4,6-triacetylphloroglucinol and study of their peroxidase mimicking activity.

Novel dibasic Schiff bases with three tridentate sites were obtained from the condensation of the triketone 2,4,6-triacetylphloroglucinol (H3ptk) with four different hydrazides, benzoyl hydrazide (bhz), furoyl hydrazide (fah), isonicotinoyl hydrazide (inh) and nicotinoyl hydrazide (nah): H6ptk(bhz)3I, H6ptk(fah)3II, H6ptk(inh)3III and H6ptk(nah)3IV. These ligand precursors I-IV, each being an ONO donor, are tricompartmental building blocks able to form trinuclear complexes having C3 symmetry. The reaction of I-IV with [VIVO(acac)2] leads to the formation of [{VIVO(H2O)}3(ptk(bhz)3)] 1, [{VIVO(H2O)}3(ptk(fah)3)] 2, [{VIVO(H2O)}3(ptk(inh)3)] 3, and [{VIVO(H2O)}3(ptk(nah)3)] 4. In methanol/aqueous solutions of M2CO3 (M+ = Na+, K+ and Cs+), these complexes are slowly converted into dioxidovanadium(v) compounds, namely, M3[(VVO2)3{ptk(bhz)3}]·6H2O [M+ = K+5, Na+9, Cs+13], M3[(VVO2)3{ptk(fah)3}]·6H2O [M+ = K+6, Na+10, Cs+14], M3[(VVO2)3{ptk(inh)3}]·6H2O [M+ = K+7, Na+11, Cs+15] and M3[(VVO2)3{ptk(nah)3}]·6H2O [M+ = K+8, Na+12, Cs+16]. All ligand precursors and complexes are characterized by various techniques such as FT-IR, UV/Visible, EPR, NMR (1H, 13C and 51V), elemental analysis, thermal studies, cyclic voltammetry (CV) and single-crystal X-ray analysis. X-ray diffraction studies of complexes K2.7[{(VVO2)3ptk(fah)3}]·11.5H2O·MeOH 6a, Cs3[{(VVO2)3ptk(bhz)3}]·7H2O 13a and Cs3[{(VVO2)3ptk(nah)3}]·7.3H2O 16a reveal their distorted square pyramidal geometry by coordinating through phenolate oxygen (of ptk), azomethine nitrogen and enolate oxygen (of hydrazide) atoms. The reactivity of complexes 5-16 and their catalytic potential were screened towards their peroxidase mimetic activity in the oxidation of dopamine to aminochrome driven by H2O2 as an oxidant. The conversion of dopamine to aminochrome with different catalysts was monitored by HPLC showing high activity under mild conditions with good conversions within 1 h. Kinetic studies using compounds 13-16 as catalyst precursors reveal that the reaction follows a Michaelis-Menten-like kinetics.

A study of DNA/BSA interaction and catalytic potential of oxidovanadium(v) complexes with ONO donor ligands.

The study of DNA/BSA interaction and the catalytic potential of four mononuclear oxidoalkoxido vanadium(v) [VVO(L1-4)OEt] (1-4) and one dinuclear oxidoalkoxido mixed-ligand vanadium(v) [{VO(L2)OEt}2(Q)]{Q = 4,4'-bipyridine}(5) complexes, with tridentate binegative aroylazine ligands are reported [where H2L1 = anthranylhydrazone of 2-hydroxy-1-napthaldehyde, H2L2 = salicylhydrazone of 2-hydroxy-1-napthaldehyde, H2L3 = benzoylhydrazone of 2-hydroxy-1-acetonaphthone, H2L4 = anthranylhydrazone of 2-hydroxy-1-acetonaphthone]. All the complexes are characterized by elemental analysis as well as various spectroscopic techniques. Single crystal X-ray diffraction crystallography of 2 reveals that the metal centre is in distorted square pyramidal geometry with O4N coordination spheres, whereas 5 exhibits a distorted octahedral geometry around the metal center. In addition, all the complexes (1-5) show moderate DNA binding propensity which is investigated using UV-vis absorption titration, circular dichroism, thermal denaturation and fluorescence spectral studies. The experimental results show that the complexes effectively interact with CT-DNA through both minor and major groove binding modes, with binding constants ranging from 104-105 M-1. Among 1-5, complexes 3 and 4 show higher binding affinity towards CT-DNA than others and at the same time also exhibit negative ΔTm values of about ∼1.5 and 1.0 °C which resembles the properties shown by cisplatin. All complexes show moderate photo-induced cleavage of pUC19 supercoiled plasmid DNA with complex 3 showing the highest photo induced DNA cleavage activity of ∼48%. In coherence with the DNA interaction studies, 3 and 4 also exhibit good binding affinity towards BSA in the range of 1010-1011 M-1, which is also supported by their ability to quench the tryptophan fluorescence emission spectra of BSA. All the complexes show remarkable photo-induced BSA cleavage activity (>90%) at a complex concentration of 50 µM. The catalytic potential of 1-5 is also tested for the oxidative bromination of styrene, salicylaldehyde and oxidation of methyl phenyl sulphide. All the reactions show a high percentage of conversion (>90%) with a high turnover frequency (TOF). Particularly, in the oxidative bromination of styrene the percentage of conversion and TOF vary from 96-98% and 8000-19 600 (h-1) respectively, which signifies the potential of these oxidovanadium(v) complexes to stimulate research for the synthesis of a better catalyst.

Vanadium(iv and v) complexes of pyrazolone based ligands: Synthesis, structural characterization and catalytic applications.

The ONO donor ligands obtained from the condensation of 4-benzoyl-3-methyl-1-phenyl-2-pyrazoline-5-one (Hbp) with benzoylhydrazide (H2bp-bhz I), furoylhydrazide (H2bp-fah II), nicotinoylhydrazide (H2bp-nah III) and isonicotinoylhydrazide (H2bp-inh IV), upon treatment with [VIVO(acac)2], lead to the formation of [VIVO(bp-bhz)(H2O)] 1, [VIVO(bp-fah)(H2O)] 2, [VIVO(bp-nah)(H2O)] 3 and [VIVO(bp-inh)(H2O)] 4, respectively. At neutral pH the in situ generated aqueous K[H2VVO4] reacts with ligands I and II, forming potassium salts, K(H2O)2[VVO2(bp-bhz)] 5 and K(H2O)2[VVO2(bp-fah)] 6, while ligands III and IV give neutral complexes, [VVO2(Hbp-nah)] 9 and [VVO2(Hbp-inh)] 10, respectively. Acidification of aqueous solutions of 5 and 6 with HCl also gives neutral complexes [VVO2(Hbp-bhz)] 7 and [VVO2(Hbp-fah)] 8, respectively. Complexes 1-4, upon slow aerial oxidation in methanol, convert into monooxidovanadium(v) complexes, [VVO(bp-bhz)(OMe)] 11, [VVO(bp-fah)(OMe)] 12, [VVO(bp-nah)(OMe)] 13 and [VVO(bp-inh)(OMe)] 14, respectively. All complexes were characterized by various spectroscopic techniques like FT-IR, UV-visible, EPR (for complexes 1-4) and NMR (1H, 13C and 51V), elemental analysis, thermogravimetry and single crystal X-ray diffraction (for complexes 5-10 and 12). In the solid state, all complexes characterized by X-ray diffraction show the metal ion 5-coordinated in a distorted square pyramidal geometry. Complexes 11-14 were tested as catalysts for the one-pot three-component (ethylacetoacetate, benzaldehyde and ammonium acetate) dynamic covalent assembly, via Hantzsch reaction, using hydrogen peroxide as oxidant in solution and under solvent-free conditions. The complexes are also active catalysts for the oxidation of tetralin to tetralone with H2O2 as oxidant. The influence of the amounts of catalyst and oxidant, and solvent, temperature and time on the catalyzed reactions was investigated.

Electron deficient nonplanar ß-octachlorovanadylporphyrin as a highly efficient and selective epoxidation catalyst for olefins.

We have synthesized 2,3,7,8,12,13,17,18-octachloro-meso-tetraphenylporphyrinatooxidovanadium(iv) (VOTPPCl8) and characterized by various spectroscopic (UV-Vis, IR and EPR) techniques, MALDI-TOF mass spectrometry and elemental analysis. The DFT optimized structure of VOTPPCl8 in CH3CN exhibited a highly nonplanar saddle shape conformation of the porphyrin macrocycle. The cyclic voltammogram of VOTPPCl8 showed a 500 mV anodic shift in the first ring reduction potential and 220 mV in the first ring oxidation potential compared to VOTPP indicating the electron deficient nature of the porphyrin π-system and further proving the existence of a nonplanar conformation of the macrocycle in solution. Further, VOTPPCl8 exhibited very high thermal stability till 390 °C as indicated in its thermogram. The oxidation state of the metal ion (V(IV)) was confirmed by EPR spectroscopy and VOTPPCl8 exhibited an axial spectrum which corresponds to the axially compressed dxy(1) configuration. VOTPPCl8 was utilised for the selective epoxidation of various olefins in good yields with very high TOF numbers (6566-9650 h(-1)) in the presence of H2O2 as an oxidant and NaHCO3 as a promoter in a CH3CN/H2O mixture. The oxidoperoxidovanadium(v) species is expected to be the intermediate during the catalytic reaction which is probed by (51)V NMR spectroscopy and MALDI-TOF mass analysis. Notably, VOTPPCl8 is stable after the catalytic reaction and doesn't form a µ-oxo dimer due to the highly electron deficient nonplanar porphyrin core and can be reused for several cycles.

Vanadium(V) complexes of a tripodal ligand, their characterisation and biological implications.

The reaction of the tripodal tetradentate dibasic ligand 6,6'-(2-(pyridin-2-yl)ethylazanediyl)bis(methylene)bis(2,4-di-tert-butylphenol), H2L(1)I, with [V(IV)O(acac)2] in CH3CN gives the V(V)O-complex, [V(V)O(acac)(L(1))] 1. Crystallisation of 1 in CH3CN at ∼0 °C gives dark blue crystals of 1, while at room temperature it affords dark green crystals of [{V(V)O(L(1))}2µ-O] 3. Upon prolonged treatment of 1 in MeOH, [V(V)O(OMe)(MeOH)(L(1))] 2 is obtained. All three complexes were analysed by single-crystal X-ray diffraction, depicting a distorted octahedral geometry around vanadium. In the reaction of H2L(1) with V(IV)OSO4 partial hydrolysis of the tripodal ligand results in the elimination of the pyridyl fragment of L(1) and the formation of H[V(V)O2(L(2))] 4 containing the ONO tridentate ligand 6,6'-azanediylbis(methylene)bis(2,4-di-tert-butylphenol), H2L(2)II. Compound 4, which was not fully characterised, undergoes dimerization in acetone yielding the hydroxido-bridged [{V(V)O(L(2))}2µ-(OH)2] 5 having a distorted octahedral geometry around each vanadium. In contrast, from a solution of 4 in acetonitrile, the dinuclear compound [{V(V)O(L(2))}2µ-O] 6 is obtained, with a trigonal bipyramidal geometry around each vanadium. The methoxido complex 2 is successfully employed as a functional catechol-oxidase mimic in the oxidation of catechol to o-quinone under air. The process was confirmed to follow a Michaelis-Menten type kinetics with respect to catechol, the Vmax and KM values obtained being 7.66 × 10(-6) M min(-1) and 0.0557 M, respectively, and the turnover frequency is 0.0541 min(-1). A similar reaction with the bulkier 3,5-di-tert-butylcatechol proceeded at a much slower rate. Complex 2 was also used as a catalyst precursor for the oxidative bromination of thymol in aqueous medium. The selectivity shows quite interesting trends, namely when not using excess of the primary oxidizing agent, H2O2, the para mono-brominated product corresponds to ∼93% of the products and no dibromo derivative is formed.

Palladium(II) complexes of OS donor N-(di(butyl/phenyl)carbamothioyl)benzamide and their antiamoebic activity.

Two promising palladium(II) compounds of general formula, cis-[Pd(L-O,S)2] [where HL-O,S = N-(di(butyl/phenyl)carbamothioyl)benzamide] as metal based antiamoebic drug candidates, have been synthesized. Both complexes are characterized in the solid state by FT-IR spectroscopy, TGA and single crystal X-ray study, as well as in solution by other spectroscopic techniques such as (1)H and (13)C NMR, and UV-visible. All these studies confirm the coordination of ligands through oxygen and sulphur atoms upon thioenolization induced delocalization. Complexes adopt cis-configuration in the solid state. Both the complexes and their respective ligands were screened in vitro for antiamoebic activity against HM1:1MSS strain of Entamoeba histolytica by microdilution method and cell viability in response to drugs was checked by using MTT assay. The IC50 values in the range 0.30-0.80 µM for ligands as well as complexes compared to 1.40 for metronidazole along with their similar inhibitory effect on cell viability of HEK293 cells like metronidazole make them promising future antiamoebic drugs.

Mimicking peroxidase activity by a polymer-supported oxidovanadium(IV) Schiff base complex derived from salicylaldehyde and 1,3-diamino-2-hydroxypropane.

The polymer-supported oxidovanadium(IV) complex PS-[V(IV)O(sal-dahp)] (2) (PS=chloromethylated polystyrene crosslinked with 5% divinylbenzene, and H3sal-dahp=dibasic pentadentate ligand derived from salicylaldehyde and 1,3-diamino-2-hydroxypropane) was prepared from the corresponding monomeric oxidovanadium(IV) complex [V(IV)O(Hsal-dahp)(DMSO)] (1), characterized and successfully used as catalyst for the peroxidase-like oxidation of pyrogallol. The oxidation of pyrogallol to purpurogallin with PS-[V(IV)O(sal-dahp)] (2) was achieved under mild conditions at pH7 buffered solution. Plausible intermediate species formed during peroxidase mimicking experiments are proposed, by studying the model complex [V(IV)O(Hsal-dahp)(DMSO)] (1) by UV-visible and (51)V NMR spectroscopies. The high peroxidase mimicking ability of polymer-supported complex 2, its stability in a wide pH range, the easy separation from the reaction media, and the reusability without considerable decrease in activity, suggest that this heterogeneous catalyst has high potential for application in sustainable industrial catalysis.

Oxidovanadium(IV) and dioxidovanadium(V) complexes of hydrazones of 2-benzoylpyridine and their catalytic applications.

Reactions between the tridentate ONN donor ligands, Hbzpy-tch () and Hbzpy-inh (), with [V(IV)O(acac)2] in dry methanol give two different types of complexes, [V(IV)O(acac)(bzpy-tch)] () and [V(IV)O(OMe)(bzpy-inh)] (), respectively. Irrespective of their nature in methanol upon aerial oxidation and precipitation both yield dinuclear [{V(V)O(bzpy-tch)}2(µ-O)2] () and [{V(V)O(bzpy-inh)}2(µ-O)2] (). Treatment of or in methanol with H2O2 yields the oxidomonoperoxidovanadium(v) complexes [{V(V)O(bzpy-tch)}2(µ-O2)2] () and [V(V)O(O2)(bzpy-inh)] (). Reactions of and with imidazolomethylpolystyrene cross-linked with 5% divinylbenzene (PS-im) in DMF give the polymer-supported PS-im[V(V)O2(bzpy-inh)] () and PS-im[V(V)O2(bzpy-tch)] (). The compounds are characterized by various spectroscopic techniques and compounds and were also analyzed by thermal, atomic force microscopy (AFM), field-emission scanning electron micrographs (FE-SEM) as well as energy dispersive X-ray (EDAX) studies. The molecular structures of and of [V(V)O(O2)(bzpy-inh)(H2O)]·0.5MeOH () were determined by single-crystal X-ray diffraction, confirming the µ-bis(O) and ONN binding mode in the dinuclear complexes and , as well as the side-on coordination of the peroxido ligand in and . The polymer-grafted compounds and were used for the catalytic oxidation of isoeugenol using aqueous H2O2 as an oxidant. The intermediate peroxido species, expected to be involved during catalytic action, were also generated from solutions of and studied by UV-Vis and (51)V NMR. The catalytic activity of the several systems was tested and the polymer-supported versions showed higher conversions than their neat counterparts. The polymer-supported complexes allow for recyclable catalytic systems, thus providing additional advantages over their homogeneous counterparts in terms of increased catalyst lifetime and easier separation from the reaction mixture.

Hydroxyquinoline derived vanadium(IV and V) and copper(II) complexes as potential anti-tuberculosis and anti-tumor agents.

Several mixed ligand vanadium and copper complexes were synthesized containing 8-hydroxyquinoline (8HQ) and a ligand such as picolinato (pic(-)), dipicolinato (dipic(2-)) or a Schiff base. The complexes were characterized by spectroscopic techniques and by single-crystal X-ray diffraction in the case of [V(V)O(L-pheolnaph-im)(5-Cl-8HQ)] and [V(V)O(OMe)(8HQ)2], which evidenced the distorted octahedral geometry of the complexes. The electronic absorption data showed the presence of strong ligand to metal charge transfer bands, significant solvent effects, and methoxido species in methanol, which was further confirmed by (51)V-NMR spectroscopy. The structures of [Cu(II)(dipic)(8HQ)]Na and [V(IV)O(pic)(8HQ)] were confirmed by EPR spectroscopy, showing only one species in solution. The biological activity of the compounds was assessed through the minimal inhibitory concentration (MIC) of the compounds against Mycobacterium tuberculosis (Mtb) and the cytotoxic activity against the cisplatin sensitive/resistant ovarian cells A2780/A2780cisR and the non-tumorigenic HEK cells (IC50 values). Almost all tested vanadium complexes were very active against Mtb and the MICs were comparable to, or better than, the MICs of drugs, such as streptomycin. The activity of the complexes against the A2780 cell line was dependent on incubation time presenting IC50 values in the 3-14 µM (at 48 h) range. In these conditions, the complexes were significantly (*P<0.05-**P<0.001) more active than cisplatin (22 µM), in the A2780 cells and even surpassing its activity in the cisplatin-resistant cells A2780cisR (2.4-8 µM vs. 75.4; **P<0.001). In the non-tumorigenic HEK cells poor selectivity toward cancer cells for most of the complexes was observed, as well as for cisplatin.

Vanadium complexes having [VO]2+, [VO]3+ and [VO2]+ cores with hydrazones of 2,6-diformyl-4-methylphenol: synthesis, characterization, reactivity, and catalytic potential.

The Schiff bases H3dfmp(L)2 obtained by the condensation of 2,6-diformyl-4-methylphenol and hydrazones [L = isonicotinoylhydrazide (inh), nicotinoylhydrazide (nah) and benzoylhydrazide (bhz)] are prepared and characterized. By reaction of [V(IV)O(acac)2] and the H3dfmp(L)2 in methanol the V(IV)O-complexes [V(IV)O{Hdfmp(inh)2}(H2O)] (1), [V(IV)O{Hdfmp(nah)2}(H2O)] (2) and [V(IV)O{Hdfmp(bhz)2}(H2O)] (3) were obtained. Upon their aerial oxidation in methanol [V(V)O(OMe)(MeOH){Hdfmp(inh)2}] (4), [V(V)O(OMe)(MeOH){Hdfmp(nah)2}] (5) and [V(V)O(OMe)(MeOH){Hdfmp(bhz)2}] (6) were isolated. In the presence of KOH, oxidation of 1-3 results in the formation of [V(V)O2{H2dfmp(inh)2}]n·5H2O (7), K[V(V)O2{Hdfmp(nah)2}] (8) and K[V(V)O2{Hdfmp(bhz)2}] (9). All compounds are characterized in the solid state and in solution, namely by spectroscopic techniques (IR, UV-Vis, EPR, (1)H, (13)C and (51)V NMR), and DFT is also used to calculate the V(IV) hyperfine coupling constants of V(IV)-compounds and (51)V NMR chemical shifts of several V(V)-species and assign them to those formed in solution. Single crystal X-ray analysis of [V(V)O(OMe)(MeOH){Hdfmp(bhz)2}] (6) and [V(V)O2{H2dfmp(inh)2}]n·5H2O (7) confirm the coordination of the ligand in the dianionic (ONO(2-)) enolate tautomeric form, one of the hydrazide moieties remaining non-coordinated. In the case of 7 the free N(pyridine) atom of the inh moiety coordinates to the other vanadium center yielding a polynuclear complex in the solid state. It is also demonstrated that the V(V)O2-complexes are catalyst precursors in the oxidative bromination of styrene by H2O2, therefore acting as functional models of vanadium dependent haloperoxidases. Plausible intermediates involved in the catalytic process are established by UV-Vis, (51)V NMR and DFT studies.

Synthesis, characterization, reactivity and catalytic activity of oxidovanadium(IV), oxidovanadium(V) and dioxidovanadium(V) complexes of benzimidazole modified ligands.

The reaction between [V(IV)O(acac)(2)] and the ONN donor Schiff base obtained by the condensation of pyridoxal and 2-aminoethylbenzimidazole (Hpydx-aebmz, I) or 2-aminomethylbenzimidazole (Hpydx-ambmz, II) in equimolar amounts results in the formation of [V(IV)O(acac)(pydx-aebmz)] 1 and [V(IV)O(acac)(pydx-ambmz)] 2, respectively. The aerobic oxidation of the methanolic solution of 1 yielded [V(V)O(2)(pydx-aebmz)] 3 and its reaction with aqueous H(2)O(2) gave the oxidoperoxidovanadium(v) complex, [V(V)O(O(2))(pydx-aebmz)] 4. The formation of 4 in solution is also established by titrations of methanolic solutions of 1 with H(2)O(2). By titrating solutions of 3 and of 4 with aqueous H(2)O(2) several distinct V(V)-pydx-aebmz species also containing the peroxido ligand are detected. The full geometry optimization of all species envisaged was done using DFT methods for suitable model complexes. The (51)V NMR chemical shifts (δ(V)) have also been calculated, the theoretical data being used to support assignments of the experimental chemical shifts. The (51)V hyperfine coupling constants are calculated for 1, the obtained values being in good agreement with the experimental EPR data. Reaction between the V(IV)O(2+) exchanged zeolite-Y and Hpydx-aebmz and Hpydx-ambmz in refluxing methanol, followed by aerial oxidation results in the formation of the encapsulated V(V)O(2)-complexes, abbreviated herein as [V(V)O(2)(pydx-aebmz)]-Y 5 and [V(V)O(2)(pydx-ambmz)]-Y 6. The molecular structure of 1, determined by single crystal X-ray diffraction, confirms its distorted octahedral geometry with the ONN binding mode of the tridentate ligand, with one acetylacetonato group remaining bound to the V(IV)O-centre. Oxidation of styrene is investigated using some of these complexes as catalyst precursors with H(2)O(2) as oxidant. Under optimised reaction conditions for the conversion of styrene in acetonitrile, a maximum of 68% conversion of styrene (with [V(V)O(2)(pydx-aebmz)]-Y) and 65% (with [V(V)O(2)(pydx-ambmz)]-Y) is achieved in 6 h of reaction time. The selectivity of the various products is similar for both catalysts and follows the order: benzaldehyde (ca. 55%) > 1-phenylethane-1,2-diol > benzoic acid > styrene oxide > phenyl acetaldehyde. Speciation of the systems and plausible intermediates involved in the catalytic oxidation processes are established by UV-Vis, EPR, (51)V NMR and DFT studies. Both non-radical (Sharpless) and radical mechanisms of the olefin oxidations were theoretically studied, and the radical pathway was found to be even more favorable than the Sharpless mechanism.

Polymer-bound oxidovanadium(IV) and dioxidovanadium(V) complexes as catalysts for the oxidative desulfurization of model fuel diesel.

The Schiff base (Hfsal-dmen) derived from 3-formylsalicylic acid and N,N-dimethyl ethylenediamine has been covalently bonded to chloromethylated polystyrene to give the polymer-bound ligand, PS-Hfsal-dmen (I). Treatment of PS-Hfsal-dmen with [V(IV)O(acac)(2)] in the presence of MeOH gave the oxidovanadium(IV) complex PS-[V(IV)O(fsal-dmen)(MeO)] (1). On aerial oxidation in methanol, complex 1 was oxidized to PS-[V(V)O(2)(fsal-dmen)] (2). The corresponding neat complexes, [V(IV)O(sal-dmen)(acac)] (3) and [V(V)O(2)(sal-dmen)] (4) were similarly prepared. All these complexes are characterized by various spectroscopic techniques (IR, electronic, NMR, and electron paramagnetic resonance (EPR)) and thermal as well as field-emission scanning electron micrographs (FE-SEM) studies, and the molecular structures of 3 and 4 were determined by single crystal X-ray diffraction. The EPR spectrum of the polymer supported V(IV)O-complex 1 is characteristic of magnetically diluted V(IV)O-complexes, the resolved EPR pattern indicating that the V(IV)O-centers are well dispersed in the polymer matrix. A good (51)V NMR spectrum could also be measured with 4 suspended in dimethyl sulfoxide (DMSO), the chemical shift (-503 ppm) being compatible with a VO(2)(+)-center and a N,O binding set. The catalytic oxidative desulfurization of organosulfur compounds thiophene, dibenzothiophene, benzothiophene, and 2-methyl thiophene (model of fuel diesel) was carried out using complexes 1 and 2. The sulfur in model organosulfur compounds oxidizes to the corresponding sulfone in the presence of H(2)O(2). The systems 1 and 2 do not loose efficiency for sulfoxidation at least up to the third cycle of reaction, this indicating that they preserve their integrity under the conditions used. Plausible intermediates involved in these catalytic processes are established by UV-vis, EPR, (51)V NMR, and density functional theory (DFT) studies, and an outline of the mechanism is proposed. The (51)V NMR spectra recorded for solutions in methanol confirm that complex 4, on treatment with H(2)O(2), is able to generate peroxo-vanadium(V) complexes, including quite stable protonated peroxo-V(V)-complexes [V(V)O(O)(2)(sal-dmen-NH(+))]. The (51)V NMR and DFT data indicate that formation of the intermediate hydroxido-peroxo-V(V)-complex [V(V)(OH)(O(2))(sal-dmen)](+) does not occur, but instead protonated [V(V)O(O)(2)(sal-dmen-NH(+))] complexes form and are relevant for catalytic action.

Vanadium complexes having [V(IV)O](2+) and [V(V)O(2)](+) cores with binucleating dibasic tetradentate ligands: Synthesis, characterization, catalytic and antiamoebic activities.

Binucleating hydrazones CH(2)(H(2)sal-bhz)(2) (I) and CH(2)(H(2)sal-fah)(2) (II), derived from 5,5'-methylbis(salicylaldehyde) and benzoylhydrazide or 2-furoylhydrazide, react with [V(IV)O(acac)(2)] to give dinuclear V(IV)O-complexes [CH(2){V(IV)O(sal-bhz)(H(2)O)}(2)] 1 and [CH(2){V(IV)O(sal-fah)(H(2)O)}(2)] 4, respectively. In the presence of KOH or CsOH.H(2)O, oxidation of 1 and 2 results in the formation of dioxidovanadium(v) complexes, K(2)[CH(2){V(V)O(2)(sal-bhz)}(2)].2H(2)O 2, K(2)[CH(2){V(V)O(2)(sal-fah)}(2)].2H(2)O 5, Cs(2)[CH(2){V(V)O(2)(sal-bhz)}(2)].2H(2)O 3 and Cs(2)[CH(2){V(V)O(2)(sal-fah)}(2)].2H(2)O 6. These complexes have also been prepared by aerial oxidation of in situ prepared oxidovanadium(iv) complexes 1 and 4. The compounds were characterized by IR, electronic, EPR, (1)H, (13)C and (51)V NMR spectroscopy, elemental analyses and thermogravimetric patterns. Single crystal X-ray analysis of 3 confirms the coordination of the ligand in the dianionic (ONO(2-)) enolate tautomeric form. The V(V)O(2)-complexes were used to catalyze the oxidative bromination of salicylaldehyde, therefore acting as functional models of vanadium dependent haloperoxidases, in aqueous H(2)O(2)/KBr in the presence of HClO(4) at room temperature. It is shown that the V(IV)O-complexes [CH(2){V(IV)O(sal-bhz)(H(2)O)}(2)] 1 and [CH(2){V(IV)O(sal-fah)(H(2)O)}(2)] 4 are catalyst precursors for the catalytic oxidation of organic sulfides using aqueous H(2)O(2). Plausible intermediates involved in these catalytic processes are established by UV-Vis, EPR and (51)V NMR studies. The vanadium complexes along with ligands I and II are also screened against HM1:1MSS strains of Entamoeba histolytica, the results showing that the IC(50) values of compounds 3 and 6 are lower than that of metronidazole. The toxicity studies against human cervical (HeLa) cancer cell line also showed that although compounds 3 and 6 are more toxic than metronidazole towards this cell line, the corresponding IC(50) values are relatively high, the cell viability therefore not being much affected.

Polymer-bound oxidovanadium(IV) and dioxidovanadium(V) complexes: synthesis, characterization and catalytic application for the hydroamination of styrene and vinyl pyridine.

The Schiff base (Hfsal-aepy) derived from 3-formylsalicylic acid and 2-(2-aminoethyl)pyridine has been covalently bonded to chloromethylated polystyrene cross-linked with 5% divinylbenzene (PS-Hfsal-aepy). Treatment of [V(IV)O(acac)(2)] with PS-Hfsal-aepy in dimethylformamide (DMF) gave the oxidovanadium(IV) complex PS-[V(IV)O(fsal-aepy)(acac)] 1, which on oxidation yielded the dioxidovanadium(V) PS-[V(V)O(2)(fsal-aepy)] 2 complex. The corresponding neat complexes, [V(IV)O(sal-aepy)(acac)] 3 and [V(V)O(2)(sal-aepy)] 4 have also been prepared. The compounds are characterized in solid state and in solution, namely by spectroscopic techniques (IR, UV-Vis, EPR, (1)H, (13)C and (51)V NMR), thermal as well as field-emission scanning electron micrograph (FE-SEM) studies. The crystal and molecular structure of [V(IV)O(sal-aepy)(acac)] was solved by single-crystal X-ray diffraction. It is a monomeric complex with the tridentate sal-aepy ligand bound equatorially and the two O-atoms of acac(-) bound at equatorial and axial positions. These complexes catalyze the hydroamination of styrene and vinyl pyridine with amines (aniline and diethylamine) yielding a mixture of two hydroaminated products in good yield. Amongst the two hydroaminated products, the anti-Markovnikov product is favored over the Markovnikov one. Plausible intermediates involved in these catalytic processes are established by UV-Vis, EPR and (51)V NMR studies, and an outline of the mechanism is proposed. The EPR spectrum of the polymer supported V(IV)O-complex 1 is characteristic of a magnetically diluted V(IV)O-complex, the resolved EPR pattern indicating that the oxidovanadium(IV) centers are well dispersed in the polymer matrix. Neat complexes exhibit lower conversion along with lower turnover frequency as compared to their polymer-anchored analogues. The polymer-anchored heterogeneous catalysts are free from leaching during catalytic action and are recyclable.